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Flashcards in Greco 1 Deck (20)
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1
Q

List 4 factors that should be considered during formulation

A
  1. Administration route - what dosage form is appropriate
  2. Potency
  3. Physio-chemical characteristics - of API (water solubility, LogP) and in relaltion to excipients
  4. Stability - greater stability = longer shelf life
2
Q

Explain powders as a formulation

A
  • Solid particles
  • Generally heterogeneous system = particles different sizes
  • Widely used in pharmaceutics as intermediates leading to other dosage forms
3
Q

List 3 characteristics of a powder

A
  1. Size (volume, shape, SA)
  2. Density
  3. Flowability
4
Q

List the 2 methods used to obtain powders

A
  1. Chemical-physical methods = clarification

2. Mechanical methods = milling (size reduction) then sieving to select powders of desired size

5
Q

What is clarification?

A

Processes aiming at removing or separating solid from a fluid (liquid or gas)
Made up of filtration and centrifugation
Either to recover the pure liquid or the solid

6
Q

List 4 mechanisms of filtration

A
  1. Straining/sieving
  2. Impingement
  3. Attractive forces
  4. Autofiltration
7
Q

Explain straining/sieving as a mechanism of filtration

A

Pores big enough to allow liquid particles through but not solid particles
However may have to pause to clear solid if large quantities

8
Q

Explain impingement as a mechanism of filtration

A

Some fluid hits the fibre with enough momentum to get retained by/stuck on the fibre
This will not happen to all particles on the same fibre - further fibres will get the rest

9
Q

Explain using attractive forces as a mechanism of filtration

A

Depends on the material being filtered and the filter material
e.g electrostatic interactions

10
Q

Explain autofiltration as a mechanism of filtration

A

Material being filtered starts filtering itself

Powder deposits on filter = cake and acts as a filter itself

11
Q

List the 4 key parameters of filtering elements

A
  1. Capacity =m the mass that can filter through a given filter before it gets blocked up
  2. Efficiency = how good a filter is at retaining a certain paritcle size
  3. Degree of filtration = smallest particle size that a filter can retain
  4. Porosity = ratio of volume of pores:total volume of filtration
12
Q

What is Darcy’s equation used to calculate?

A

The rate of filtration

13
Q

What is Darcy’s equation?

A

V/t = (K x A x ΔP) / μ x L

14
Q

What do the symbols in Darcy’s equation represent?

A
V/t = volume/time
K = constant, depends on porosity of filtering element
A = area of filter
ΔP = difference in pressure from top of filter to bottom of filter
u = viscosity of liquid being filtered
L = thickness of filtering element plus any material already filtered
15
Q

What is the end product of centrifugation?

A

Pellet of solid at the bottom, liquid at the top

Liquid usually known as supernatant

16
Q

What is the formula to calculate the ratio of centrifugal force to gravity?

A

C = F/G

C= ratio of F/G
F = centrifugal force
G = gravity
17
Q

What is the formula to calculate centrifugal force (F)?

A

F = (mv^2)/r

F = centrifugal force
m = particle mass
v = velocity
r = radius of spinning centrifuge
18
Q

What is the formula to calculate the gravity (G)?

A

G = mg

G = gravity
m = mass
g = gravitational constant
19
Q

What is the formula to calculate velocity of the centrifuge?

A

v = pi x d x n

v = velocity
d = diameter (2r)
n = rotation speed
20
Q

Based on these equations, which factors can be changed to increase the centrifugal force/effect?

A

Radius of spinning centrifuge (r) and rotation speed (n)

However better to increase speed than diameter as n is squared in the equations = great effect on C